Reduced curl in photographic paper



United States Patent O F REDUCED CURL-IN PHOTOGRAPHIC PAPER Glen G. Gray, Rochester, assignor to Eastman Kodak Company; Rochester, N. Y;, a corporation of Newalersey No Drawing. Application December 20, 1954 Serial No. 476,547

6 Claims. 01. 117- 143 This invention relates to methods for treating paper to reduce or eliminate curl, particularly for treating photographic paper to stabilize the paper against eventual change caused by change in the humidity and the like.

Photographic papers are often coated with gelatin or vinyl compositions which have a difierent coeflicient of expansion and contraction from that of the cellulosic materials of which papers are made. Consequently, upon drying or with changes in relative humidity the papers tend to curl or to change dimensionally. Various means have been suggested for eliminating curl in photographic paper, particularly those directed to treating the gelatin layer or the photographic emulsion, to eliminate the effects caused by contraction or expansion of this surface layer. For instance, mechanical rollers or flexers have been used, but these may result in myriad small cracks in the coated surface. Steaming the support side of the print and flexing the print while in a steamed condition to reduce the effect of the mechanical treatment is disclosed in U. S. Patent 1,880,451. Various print fiattening solutions have been used which contain chemical compositions such as ethylene glycol, glycerol, diethylene glycol and the like. These compounds depend upon their hygroscopic nature to accomplish whatever benefit is obtained by their use. Furthermore, they must have an atmosphere of relatively high humidity to be efiective.

The above methods have been used for post-processing curl control usually of the paper prints immediately following the washing step in photographic processing. Following this treatment for reducing the post-processing curl, the photographic paper is often handled at low relative humidity, for instance in hot air dryers.

Other factors in the paper tend to influence and cause curl. For instance, due to the nature of the cellulose fiber from which paper is made, the paper fibers swell in water resulting in dimensional changes in the paper. Sizing agents such as rosin, gelatin and waxes used in the paper industry may reduce this tendency and also the rate of hygroexpansivity, but they have little effect on the dimensional changes of equilibrium.

Chemical treatment of photographic paper can only be undertaken with compositions which are photographically compatible with the light-sensitive emulsions to be subsequently coated on the paper. Therefore, although some compositions might be used which would accomplish the object of reducing curl in paper and rendering it dimensionally stable, these compositions would not be useful in photographic applications.

U. S. 2,673,154 issued to Gray et al. discloses the use of long-chain ethers for treating photographic prints to reduce post-processing curl. These long-chain ethers were applied to the prints prior to drying, but after the lightsensitive emulsion had been exposed and photographically processed.

Now I have made the unexpected discovery that these long-chain ethers can be used to treat the paper base prior to coating with a photographic emulsion, that these papers.

2,865,792 Patented; Dec. 23', 8

ethers are compatiple with emulsions, and that theyreduce the curl vof 'the paper during processing. Moreover, papers which are not to be used for photographic purposes, may be treated with these ethers .in orderto render them dimensionally stable and to reduce cfirl;

One object of this invention is to provide a method of treating paper to reducejcurl due to changesv in relative humidity. Another object of thisinvention is. toproyide a chemical treatment for reducing the curl of paper which is compatible with photographic emulsions. A further object is to reduce the rate ofhygroexpansivity of cellulose Anadditiohal object is to re' duce' t'he dimensional changes in paper oncontact w'ith wateifi I have discovered that long-chain ethers which may be used to achieve the objects of this invention are ethers having recurring ethoxy groups. Examples of ethers of this type are tetraethylene glycol dimethyl ether CH OCH CH OCH CH OCH CH OCH CH OCH and diethylene glycol diethyl ether CH CH OCH CH OCH CH OCH CH However, it will be observed from the description herein that certain other ethers of this type may be used and are within the scope of this invention. The following data shows the results of using these compounds as compared with untreated comparisons in which a 20-pound wood pulp paper was used:

Treatment of the paper with the glycol ether compounds was effective in reducing curl and did notstain the paper. These compounds were not photographically active.

The above examples show that long-chain plasticizers which are non-hygroscopic will reduce paper curl. The preferable concentration is 15% of the long-chain ether in water. However, concentrations may also be varied depending upon the amount of correction required and depending on the photographic emulsion which is to be used on the paper. Consequently, it may be desirable to use concentrations as high as 50% or a concentration as low as 5% depending upon the application.

From the preceding description, it is seen that longchain ethers may be used other than those described in the examples. Other long-chain, non-hygroscopic materials which may be used are ethers having a chemical composition RO(CH CH O),,R' wherein R and R are alkyl groups and n is a number larger than 2 but less than 135. Examples of compounds of this type in addition to tetraethylene glycol dimethyl ether and diethylene glycol diethyl ether are dimethoxy polyethylene glycols, diethoxy polyethylene glycols, dimethoxy polypropylene glycols, and diethoxy polypropylene glycols.

I claim:

1. A process of treating photographic paper to reduce curl, prior to coating with a photographic emulsion comprising impregnating the paper with a long-chain, nonhygroscopic organic ether having a chemical composition RO(CH CH O),,R' in which R and R are alkyl groups and n is a number between 2 and 135, followed by coating the impregnated paper with a light-sensitive photographic emulsion.

2. A process according to claim 1 in which the long chain ether is selected from the group consisting of tetraethylene glycol diethyl ether and diethylene glycol diethyl ether.

3. A process according to clairnl wherein the ether is contained in a solution in which the ether concentration is between 10% and 20% by weight. I

4. A process according to claim 3 wherein the impregnating solution applied comprises water and ether.

5. A process according to claim 1 wherein the-longchain ether is diethylene glycol diethyl ether.

6. A process according to claim 1 in which the longchain ether is tetraethylene glycol dimethyl ether.

References Cited in the file of this patent UNITED STATES PATENTS' 2,108,810 Finzel et al. Feb. 22, 1938 4 2,164,431 Schoeller et a1. July 4, 1939 2,249,118 Dewitt July 15, 1941 2,286,314 Seymour et al. June 16, 1942 2,419,206 Fisher Apr. 22, 1947 2,576,320 Vlad et al. Nov. 27, 1951 2,673,154 Gray et al. Mar. 23, 1954 OTHER REFERENCES Carbon and Carbides publication Ethers and Oxides," #F-4764A, pages 4 and 18.

Handbook of Chemistry and Physics, 32nd edition, Chemical Rubber Publishing Co., Cleveland, Ohio (page 

1. A PROCESS OF TREATING PHOTOGRAPHIC PAPER TO REDUCE CURL, PRIOR TO COATING WITH A PHOTOGRAPHIC EMULSION COMPRISING IMPREGNATING THE PAPER WITH A LONG-CHAIN, NONHYGROSCOPIC ORGANIC ETHER HAVING A CHEMICAL COMPOSITION RO(CH2CH2O)NR'' IN WHICH R AND R'' ARE ALKYL GROUPS AND N IS A NUMBER BETWEEN 2 AND 135, FOLLOWED BY COATING THE IMPREGNATED PAPER WITH A LIGHT-SENSITIVE PHOTOGRAPHIC EMULSION. 